Wheels-on brake drum gage

Abstract

A brake drum gage is described for measuring the inside diameter of a brake drum of a vehicle with the wheel mounted on the vehicle in the presence of an axle tube and other undercarriage components or parts. The brake drum gage includes an elongate generally flat bar having proximate and remote ends and defines an elongate axis in a reference plane. A fixed element is fixedly mounted at the proximate end of the bar and a movable element is movably mounted on the bar for movements along the bar between the proximate and remote ends for adjusting the spacing between these elements. Each element includes a generally V-shaped arm that includes an upright portion generally parallel to the reference plane and an angled portion inclined in relation to an associated upright portion. A fixed anvil is provided on the angled portion of the fixed element and has a tip extending beyond the fixed element in a direction of the remote end of the bar and the movable anvil is provided on the angled portion of the movable element and has a tip extending beyond the movable element in a direction of the proximate end of the bar. An indicator in the form of an electronic digital module is provided for providing an indication of the distance between the tips of the anvils along the direction substantially parallel to the axis. The anvils on the angled portions are positionable at diametrically opposite positions of the inside cylindrical surface of the brake drum while the bar is spaced inwardly from the drum and clear of the axle tube and other undercarriage components or parts of the vehicle. Adjustable depth stops are provided on the angled portions of both elements to ensure accurate positioning of the anvils at diametrically opposite points of the cylindrical surface to be measured. In this manner the brake drum gage can be used to accurately measure brake drums without removing the wheels from a vehicle.

What we claim is:  
     
       1. A brake drum gage for measuring an inside diameter of a brake drum of a vehicle with a wheel mounted on the vehicle in a presence of an axle tube and other undercarriage components or parts, comprising an elongate generally flat bar having proximate and remote ends and defining an elongate axis and reference plane; a fixed element fixedly mounted at said proximate end of said bar and a movable element movably mounted on said bar for movements along said bar between proximate and remote ends for adjusting a spacing between said elements, each element including a generally V-shaped arm including an upright portion generally parallel to said reference plane and an angled portion inclined an angle α in relation to said reference plane of said flat bar; a fixed anvil on said angled portion of said fixed element and having a tip extending beyond said fixed element in a direction of said proximate end of said bar and a movable anvil on said angled portion of said movable element and having a tip extending beyond said movable element in a direction of said remote end of said bar; indicating means for providing an indication of a distance between the tips of said anvils on said angled portions being positionable at diametrically opposition positions on an inside cylindrical surface of a brake drum while said bar is spaced inwardly from said drum and clears the axle tube and other undercarriage components or parts of the vehicle, whereby the drum gage can be used to measure brake drums without removing wheels from a vehicle. 
     
     
       2. A brake drum gage as defined in claim  1 , wherein said upright portions of said fixed and movable elements are spaced from each other in substantially parallel planes and said angled portions of said fixed and movable elements are spaced from each other in substantially parallel planes, whereby said movable portions can be positioned coextensively with or moved to both sides of said fixed portions along said axis of said bar. 
     
     
       3. A brake drum gage as defined in claim  2 , further comprising zeroing means for zeroing said indicating means when a spacing between said tips along said axis of said bar is set to zero. 
     
     
       4. A brake drum gage as defined in claim  3 , wherein said zeroing means comprises stop means for physically stopping said movable element when moved in the direction of said proximate end at a point when the distance between said tips is reduced to zero. 
     
     
       5. A brake drum gage as defined in claim  2 , wherein said fixed element comprises a fixed transverse portion secured to said proximate end of said bar and a fixed axial portion extending between said transverse portion and said upright portion of said fixed element for axiallly offsetting said upright portion in the direction of said remote end in relation to said fixed transverse portion for positioning said fixed anvil a predetermined axial distance from said remote end and to one transverse side of said bar, and said movable element comprises a movable transverse portion slidably mounted on said bar and a movable axial portion extending from said movable transverse portion in the direction of said proximate end and to said one end transverse side of said bar; stop means for stopping said movable transverse portion at a predetermined position in which said tip of said movable anvil is positioned at said predetermined axial distance along said bar to align said anvil tips along the direction of said axis, whereby movement of said movable portion towards said proximate end of said bar causes said tips to point towards each other to reflect a physical and true “zero” axial distance between said tips and said indicating means is calibrated to show a spacing of zero. 
     
     
       6. A brake drum gage as defined in claim  5 , wherein said stop means comprises an adjustment screw threadedly mounted on said fixed element for movements in the direcction of said axis and for engagement with said movable element. 
     
     
       7. A brake drum gage as defined in claim  1 , wherein α is selected from the range of 90°-135°. 
     
     
       8. A brake drum gage as defined in claim  7 , wherein 100°<α<121°. 
     
     
       9. A brake drum gage as defined in claim  8 , wherein α≈111°. 
     
     
       10. A brake drum gage as defined in claim  1 , wherein said indicating means includes an electronic digital module. 
     
     
       11. A brake drum gage as defined in claim  1 , wherein said fixed and movable elements are supported on opposite sides of said flat bar. 
     
     
       12. A brake drum gage as defined in claim  1 , wherein said fixed upright portion is approximately 6 inches long and said fixed angled portion is approximately 4 inches long, and said movable upright portion is approximately 5.7 inches long and said movable angled portion is approximately 3.5 inches long. 
     
     
       13. A brake drum gage as defined in claim  1 , wherein the lengths of said upright and angled portions are selected to maintain associated portions substantially parallel to each other when the same angles of inclination are used for said upright and angled portions of said fixed and movable elements. 
     
     
       14. A brake drum gage as defined in claim  1 , wherein said movable and fixed elements are made of aluminum. 
     
     
       15. A brake drum gage as defined in claim  14 , wherein apertures or openings are provided in said angled portions to reduce the weight of the gage. 
     
     
       16. A brake drum gage as defined in claim  15 , wherein said apertures or openings are in the form of a series of openings successively arranged along a line extending along said angled portions. 
     
     
       17. A brake drum gage as defined in claim  1 , further comprising depth stop means for selectively adjusting the extent to which said anvils on said angled portions can penetrate a cylindrical surface to be measured beyond a reference plane substantially normal to an axis of said cylindrical surface. 
     
     
       18. A brake drum gage as defined in claim  17 , wherein said depth stop means comprises a plurality of adjustable depth stops at least some of which are slidably mounted on an angled portion to move between retracted positions in which said depth stops do not restrict or limit the positions of said anvils in relation to said reference surface and extended positions in which said depth stops engage an edge or abutment surface of a drum to limit the further penetration of an associated anvil into said brake drum beyond said reference plane. 
     
     
       19. A brake drum gage as defined in claim  18 , wherein at least two adjustable depth stops are spaced from each other along each of said angled portions at different distances from an associated anvil. 
     
     
       20. A brake drum gage as defined in claim  19 , wherein a support block is provided on each angled and portion provided with spaced bores having axes substantially parallel to said axis of said bar, said adjustable depth stops comprising cylindrical pins slidably mounted in said bores.